Phillips, a conservative lionheart, regards the UN as a cynical institution that long ago dissipated its moral legitimacy. It is a place where the language of human rights is routinely hijacked by the enemies of human rights, and where democracies like America and Israel are reviled while the world’s most odious regimes are indulged. In nominating Power, says Phillips, Obama has picked a nominee with views much the same as those that prevail at the UN.

Others on the right have been equally harsh.

“Jeanne Kirkpatrick is turning in her grave right now,” Keith Urbahn, who was chief of staff under Defense Secretary Donald Rumsfeld, commented on Twitter. Texas Senator Ted Cruz sharply criticized Power’s nomination, suggesting she would be “an advocate of elevating UN interests over US sovereignty.” It is clear, wrote Commentary magazine’s Seth Mandel, “that such a person should not be anywhere near the levers of power.”

Obama’s choice of Power was bound to be contentious. With strong, critical views on foreign policy and a penchant for expressing them strongly and critically, she has left a trail of controversial statements that she should expect to be grilled on during her Senate confirmation hearings.

The objections to Power aren’t merely partisan. Some of her more intemperate remarks have been genuinely disturbing. Yet while she is a staunch liberal and a close Obama loyalist, even staunch conservatives and Obama opponents might want to think twice before deciding she doesn’t belong at the UN.

Some Americans may never have heard of Power before 2008, when she was a foreign-policy adviser on Obama’s presidential campaign and got in hot water for branding Hillary Clinton “a monster.” But she first came to prominence as a journalist writing about real human monsters — those who incite and commit genocide — and about the consistent unwillingness of American political leaders to make the prevention of mass slaughter a priority. In August 2001, The Atlantic published Power’s devastating indictment of Bill Clinton’s inertia during the Rwandan genocide. As civilians were being slaughtered by the hundreds of thousands, the US government passed up countless opportunities to stop the bloodshed, even refusing to use the term “genocide” for fear of being obliged to act.

That passivity, Power documented in her 2002 book “A Problem from Hell,” was typical of US foreign policy in the 20th century, when genocides from Armenia to the Holocaust to Cambodia raged out of control without ever rousing American policymakers to act with moral urgency. Her book, which won a Pulitzer Prize, is a searing account of what to expect when “never again” is merely a slogan. It is also a powerful refutation of the idea that the world becomes a safer place when America retreats from the global stage, preferring to “lead from behind” than to actually lead.

No surprise, then, that Power earned a reputation as an advocate of human-rights intervention — a magazine cover once dubbed her “Interventionista!” — or that she was among those who convinced Obama to deploy military force to prevent Libya’s Moammar Khadafy from carrying out a threatened slaughter.

Ironically, one of the arguments being pressed by Power’s conservative opponents is that she “shares Obama’s desire for a diminished US role in the world,” as The Wall Street Journal editorialized last week. Critics point to her 2003 essay urging US officials to institute “a doctrine of the mea culpa,” publicly apologizing for past “sins” and undertaking “a historical reckoning with crimes committed, sponsored, or permitted by the United States.”

That isn’t the only dubious passage in Power’s voluminous record. Nor is it the most offensive. Power is vehement and opinionated, and the softly-softly approach has never been her style.

But since when do conservatives think that’s a bad quality, especially in ambassadors to the United Nations? Those who savored John Bolton’s outspokenness and admired Kirkpatrick’s moral passion should relish the prospect of Power’s fervor and candor piercing the UN’s hypocritical complacency. Her political priorities may not be theirs — she is a liberal — but a US envoy unafraid to condemn the world’s most bloodthirsty regimes is something all Americans should value. On the evidence so far, Power and the UN are indeed a perfect match. And yes, that’s a compliment.